3.1 All studies evaluated the original Peristeen system, which is assumed to be equivalent to Peristeen Plus with the balloon catheter. The evidence for Peristeen assessed by the external assessment centre (EAC) comprises 13 studies in adults and 11 studies in children, plus 2 studies and 1 audit that were included specifically to provide information on adverse events. Only 1 study was a randomised controlled trial (Christensen et al. 2006); all others were observational studies. For full details of the clinical evidence, see section 3 of the assessment report. 
3.2 Christensen et al. (2006) was a randomised controlled trial in adults (n=87) that showed statistically significant improvements in bowel-related patient-reported outcomes for Peristeen compared with standard bowel care over 10 weeks' follow up. The EAC considered this to be the best quality evidence to support the use of Peristeen.
3.3 The other 12 studies in adults were observational case series (9 prospective and 3 retrospective). The EAC acknowledged that these studies have a high risk of bias because they included a broad patient population (including people with neurogenic and non-neurogenic bowel dysfunction) and often used inconsistent and non-validated outcome measures and questionnaires. Furthermore, there were high initial drop-out rates in all studies. The EAC stated that despite these uncertainties, the evidence showed that adults who choose to continue using Peristeen report improved clinical outcomes.
3.4 All the studies in children were non-comparative, observational case series (6 observational and 5 retrospective). The studies were done in a very broad patient population with a wide range of ages, types of bowel dysfunction and concurrent conditions. The studies showed improvements in some outcomes for children using Peristeen but the EAC considered the overall published evidence in children to be of low quality. Many of the patient-reported outcomes in the studies were not adapted or validated specifically for use in children, and it was often unclear if the questionnaires had been completed by the child themselves or by a carer or guardian. The EAC and clinical experts commented that these limitations are to be expected, considering that Peristeen is used in a community environment with patient or carer support, and is associated with subjective as well as objective clinical benefits that children may find difficult to describe themselves.
3.5 Bowel perforation is a serious adverse event that is potentially linked to the use of Peristeen. It was a rare complication (2 in 1 million irrigations) reported in the global audit by Christensen et al. (2016). It may be even rarer in children (1 in 1 million irrigations) as reported in a review of best practice by Mosiello et al. (2017). Other, less serious adverse events such as abdominal pain, rectal bleeding and nausea were more common. For full details of the adverse events, see section 3.7 of the assessment report. 
3.6 The cost model submitted by the company includes only adults with neurogenic bowel dysfunction as a result of a spinal cord injury. It is based on the economic methodology used in Emmanuel et al. (2016), a paper that describes a cost-effectiveness model based on an audit database from 3 UK hospitals that was set up in 2006. It is a Markov model with a 6‑month cycle and 37‑year time horizon, and assumes that patients entering the model are the same in terms of spinal injury and constant transition probabilities. It also assumes that Peristeen is used every other day (as recommended by the company), and that the comparator is standard bowel care. For full details of the economic evidence see section 3 of the assessment report.
3.7 The company did not include the audit data (on which the model was based) as part of its clinical evidence submission, and these data are not published elsewhere. However, the company provided the EAC with an extract from the data that was used for quality-of-life calculations and also provided information on length of use, and whether patients had stopped using Peristeen. The EAC considered that the audit data seemed to be taken from an appropriate NHS setting, with suitable patient pathways and an appropriate, if heterogeneous, population (227 patients aged 17 to 70 years with neurogenic bowel disease and different neurological diagnoses). However, the EAC concluded that it had not seen enough information to fully critique the audit data or its suitability for the model.
3.8 The company's base-case results showed that using Peristeen could lead to cost savings of £21,768 per patient over 37 years. However, the EAC identified limitations in the company's base case. It made a number of changes and corrections to the model, including:
incorporating the costs of standard care for people who stop using Peristeen within the Peristeen arm
adjusting transition probabilities
changing the costs of pressure ulcers and urinary tract infections
adding background mortality.
These changes decreased the cost savings associated with Peristeen to £5,267 per patient over the same period. For full details of these changes, see section 4.5 of the assessment report. [corrected 2022]
3.9 The main factors affecting these cost savings are the number of catheters used (driven by frequency of use), carer time to help with irrigation, frequency of faecal incontinence and hospitalisations (particularly for pressure ulcers).
3.10 During consultation, a healthcare professional submitted a retrospective service review that described the use of transanal irrigation and ACE procedures to treat bowel dysfunction in children (n=111) at 1 UK centre in the UK between 2007 and 2016. The review included children with a wide range of neurological and non-neurological bowel dysfunctions between 2007 and 2016. Children in the study were offered 1 of 3 devices: Peristeen (which 90% of children had) or either of 2 cone-based systems. Although 18 of the 111 children discontinued transanal irrigation during the study, 75 (68%) had restored continence or symptom resolution. The review also noted that 13 of the 68 children with constipation and soiling (19%) had been weaned off transanal irrigation and discharged from the centre. The review reported highly positive comments from parents and carers, who stated that transanal irrigation had significantly improved their child's quality of life. The EAC noted that this study would have been excluded from the literature search, because it included results from 3 devices.